In testing a semiconductor integrated circuit on a semiconductor wafer such as a silicon wafer, a special machine such as a wafer prober is used which includes a probe card having a plurality of contact pins. The contact pins establish electrical connections with electrodes on the surface of the wafer to transmit signals therebetween. FIGS. 4 and 5 show an example of structure in a conventional probe card for testing such semiconductor integrated circuits on a semiconductor wafer.
In FIG. 4, the probe card has contact pins 19, an insulation plate 17 and coaxial cables 18 for testing a semiconductor device 7 which is formed on a silicon wafer 1. The semiconductor device 7 to be tested has a plurality of electrodes 2 such as bonding pads on its surface.
The contact pins 19 in this case are called pogo pins which have an elastic function with a telescopic structure. Each of the contact pins 19 is provided to face the corresponding electrode 2 of the test device 7. The electric connection will be established when the ends of the contact pins 19 are pressed on the electrodes 2. The insulation plate 7 is to place the contact pins 19 in a predetermined position and fix the contact pins in such a position. The coaxial cables 18 are connected to the upper parts of the contact pins 19 for establishing electrical communication between the test device 7 and a test system 28 shown in a block diagram of FIG. 7.
Another example of conventional probe card is shown in FIG. 5. The probe card of FIG. 5 includes a plurality of electrode bumps 21, a membrane 20, a probe frame 22, screws 23 and coaxial cables 18. The electrode bumps 21 are provided on the surface of the membrane 20 to meet the electrodes of the test device 7 on the silicon wafer 1. In addition to the electrode bumps 21, the membrane 20 is further provided with circuit patterns connected to the bumps 21 for transmitting electric signals. Namely, the electrode bumps 21 are electrically connected with the corresponding coaxial cables 18 through the circuit patterns.
A plunger 24, screws 23, a spring 25 and a pressure sensor 26 are provided to establish up-down movements of the electrode bumps 21 and the membrane 20. Thus, the electrode bumps 21 are pressed on the electrodes to form electric connections therebetween. A probe frame 22 supports the various components noted above and allows the up-down movements of the electrode bumps 21.
The position of the electrode bumps 21 with respect to the electrodes 2 on the test device 7 is adjusted by positioning the plunger 24 in vertical and horizontal directions by the screws 23. Thus, the communication by electric signals between the semiconductor device 7 under test and a semiconductor test system 28 (FIG. 7) will be made through the coaxial cables 18.
Because of the increasing density and operation speed in the semiconductor integrated circuits, probe cards for testing the integrated circuits on the semiconductor wafer need to have contact pins with higher density and better impedance matching at the connection points. Further, because of the increasing density and the scale of the integrated circuits, the contact pins on the probe card are required to maintain the sufficient electric contact with the electrodes on the wafer even when the flatness of the wafer is fluctuated or deteriorated.
When the electrodes 2 of the test device 7 are aluminum electrodes, to secure the electric contact between the electrodes 2 and the contact pins on the probe card, it is also required to have a scrubbing function for removing an oxide film on the surface of the electrode 2. This scrubbing function is considered to maintain the sufficient electric contact with high reliability.
In the conventional probe card using the contact pins 19 shown in FIG. 4, it is possible to make the tip of the contact pin 19 small enough to match the size of the electrode 2 on the wafer. However, because the contact pin 19 needs to have a sufficient size to maintain the enough mechanical rigidity, and the spaces for connection with the coaxial cables 18 must be provided, it is considered that the minimum distance between the contact pins 19 is limited to about 1 mm pitch.
In the conventional probe card using the electrode bumps 21 on the membrane 20 as shown in FIG. 5, it, is possible to have higher density of the electrode bumps than the density of the probe card using the contact pins 19 of FIG. 4. However, the density of FIG. 5 is still limited to the order of about 0.5 mm. Further, the example of FIG. 5 is not adequate to overcome the deterioration of the flatness of the wafer surface since the electrode bump 21 is not independent from the others. By the same reason, the scrubbing function for removing the oxide film of the electrodes of the test device is not available.
Therefore, in the conventional probe card using the pogo pin type contact pins or the membrane having the bumps are not suitable to meet the requirement of the recent semiconductor integrated circuit having an ultra small pitch between the electrodes. It is necessary to develop a probe card and a contact pin structure having a new approach to overcome the dimensional limit and to meet the needs of the high density semiconductor device.